Thermally actuated switch

ABSTRACT

A thermally actuated snap-acting switch comprising a switch housing, thermal actuator means having a portion within the housing movable relative thereto in response to changes in temperature, and switch means within the housing actuatable by the thermal actuator means. The switch means includes a stationary contact, a first terminal for the stationary contact, a movable switch arm, a movable contact carried by the switch arm, and a second terminal for the movable contact. The switch arm and movable contact are movable between a first position in which the stationary and the movable contacts are in electrical contact with one another and a second position in which the contacts are spaced from one another for making and breaking an electrical circuit between the terminals. The switch means further comprises a switch frame secured to the housing and means for abruptly moving the switch arm and movable contact from their first position to their second position when the thermal actuator portion moves into a position corresponding to a predetermined temperature. The means for abruptly moving the movable contact and the switch arm comprises spring means interposed between the switch arm and the switch frame for biasing the switch arm into one of its positions and for abruptly moving the switch arm between its stated positions in response to a predetermined amount of movement of the thermal actuator portion. The abruptly movable means further comprises adjustable means for varying the temperature at which the movable contact and switch arm move abruptly over center from one position to another. The adjustable means has means for moving the switch frame and the spring means relative to the stationary contact.

United States Patent [191 Da'igneault, Jr.

[451 Aug. 12, 1975 THERMALLY ACTUATED SWITCH Theodore J. Daigneault, Jr., Sheldonville, Mass.

[73] Assignee: Texas Instruments Incorporated,

Dallas, Tex.

[75] Inventor:

[52] U.S. Cl. 337/386; 337/390; 337/392 ['51] Int. Cl. HOIH 37/74 [58] Field of Search 200/160, 67 D; 337/394,

[56] References Cited UNITED STATES PATENTS 3,004,123 10/1961 Cannon 337/388 X 3,029,329 4/1962 Bolesky 337/386 3,194,927 7/1965 Place 337/388 X 3,202,789 8/1965 Morris 337/386 3,327,946 6/1967 Benson 337/392 X Primary Examin erG. Harris Attorney, Agent, or Firm-James P. McAnclrews; John A. Haug; Russell E. Baumann [5 7] ABSTRACT A thermally actuated snap-acting switch comprising a switch housing, thermal actuator means having a portion within the housing movable relative thereto in response to changes in temperature, and switch means within the housing actuatable by the thermal actuator means. The switch means. includes a stationary contact, a first terminal for the stationary contact, a movable switch arm, a movable contact carried by the switch arm, and a second terminal for the movable contact. The switch arm and movable contact are movable between a first position in which the stationary and the movable contacts are in electrical contact with one another and a second position in which the contacts are spaced from one another for making and breaking an electrical circuit between the terminals. The switch means further comprises a switch frame secured to the housing and means for abruptly moving the switch arm and movable contact from their first ture at which the movable contact and switch arm.

move abruptly over center from one position to another. The adjustable meanshas means for moving the switch frame and the spring means relative to the stationary contact.

9 Claims, 6 Drawing Figures PATENTEU AUG 1 21975 SHEET FIG! I ,899 765 PATENTED AUG 1 2 I975 v 3 FIG.5

THERMALLY ACTUATED SWITCH BACKGROUND OF THE INVENTION This invention relates to a thermally actuated, snapacting switch, and more particularly to such a switch which may be readily adjusted (i.e., calibrated) to actuate at a predetermined temperature.

This invention is particularly concerned with a snapacting switch operable by a rod-and-tube thermal actuator which moves in response to exposure to varying temperature conditions. For example, the rod-and-tube actuator may be installed in an automotive catalytic converter. Upon the catalyst bed in the converter exceeding a specified maximum temperature, a snap acting switch is actuated by the rod-and-tube thermal actuator to initiate means for cooling the catalyst bed (e.g., opening an air bypass door) thereby to prevent damage to the catalyst bed, and/or to energize a Waming light for the operator. The maximum operating temperature of the catalyst bed is preferably limited to about l700F.

With known prior art thermally actuated switches, it was difficult to insure that these switches would reliably actuate at a specified temperature. Due to manufacturing discrepancies, similar switches might vary considerably in the temperature at which they are actuated. In addition to calibrating the switch to actuate at a desired temperature (i.e., a given trip temperature), it has also been a problem to effect automatic reset of the switch at a second selected temperature. The difference between the temperature at which the switch is actuated and the temperature at which the switch is reset is referred to as the switch differential temperature. In some applications, it is desirable that the switch reset at a particular temperature (below its trip temperature), and that this differential be relatively small. With known prior art switches, it has been difficult to calibrate or preset the trip and reset temperatures of the switch.

SUMMARY OF THE INVENTION Among the several objects of this invention may be noted the provision of a snap-acting switch for use with a rod-and-tube thermal actuator which may readily be adjusted (i.e., calibrated) to actuate at a specified temperature level; the provision of such a switch in which the contacts move abruptly between their open and closed positions thereby to prevent damage to the contacts; the provision of such a switch in which the switch differential temperature may readily be adjusted prior to assembly of the switch; the provision of such a switch in which trip temperature of the switch may be externally adjusted; the provision of such a switch which is compact and which will withstand severe environments; and the provision of such a switch which is of economical construction and which is reliable in operation. Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.

Briefly, a thermally actuated snap-acting switch of this invention comprises a switch housing, thermal actuator means having a portionwithin the housing movable relative thereto in response to changes in temperature, and switch means within the housing actuable by the thermal actuator means. The switch means comprises a stationary contact, a first terminal for the stationary contact, a movable switch arm, a movable contact carried by the switch arm, and a second terminal for the movable contact. The switch arm and movable contact are movable between a first position in which the stationary and the movable contacts are in electrical contact with one another, and a second position in which the contacts are spaced from one another for making and breaking an electrical circuit between the terminals. The switch means also includes a switch frame secured to the housing and means for abruptly moving the switch arm and the movable contact from their first position to their second position when the thermal actuator portion moves into a position corresponding to a predetermined temperature. The abovementioned means for abruptly moving the movable contact and the switch arm includes spring means interposed between the switch arm and the switch frame for biasing the switch arm into one of its positions and for abruptly moving the switch arm between these positions in response to a predetermined amount of movement of the thermal actuator portion. Adjustable means are also provided for varying the temperature at which the movable contact and the switch arm move abruptly over center from one position to another. This adjustable means includes means for moving the switch frame and the spring means relative to the stationary contact.

. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view of a snap-acting, thermally actuated switch assembly of this invention;

FIG. 2 is an enlarged vertical section of the switch assembly of FIG. 1 illustrating the contacts of the switch in their normally closed position;

FIG. 3 is a a view similar to FIG. 2 showing the contacts in their open position;

FIG. 4 is a horizontal sectional view taken on line 4-4 of FIG. 2;

FIG. 5 is a vertical section taken on line 5-5 of FIG. 2; and

FIG. 6 is a horizontal section taken on line 6-6 of FIG. 2.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, a thermally actuated snap-acting switch of this invention, indicated in its entirety at l, is shown to comprise a switch housing 3 and a thermal actuator 5 extending from the bottom of the housing. As shown in FIG. 2, housing 3 has a chamber 7 therein for reception of switch means, generally indicated at 9, actuable by the thermal actuator.

More particularly, the switch 1 of this invention, as illustrated in the drawings, is adapted for opening a circuit (i.e., it is normally closed) in response to thermal actuator 5 being exposed to a predetermined elevated temperature (e.g., 1700F. Housing 3 is preferably made of a high-temperature material, such as stainless steel, but other materials may be suitable. Housing 3 is threaded, as indicated at 10, for installation, for example, into the catalyst bed of an automotive catalytic converter.

Thermal actuator 5 is a rod-and-tube actuator having an outer tube 11 and a rod 13 within the tube. Housing 3 has an axial bore 15 through one end thereof (i.e., its bottom end) and tube 11 is inserted therethrough. As

shown in FIG. 2, the inner end of tube 11 is flanged, as indicated at 17, and the tube is secured to the housing, as by welding the flange to the inner surface of the housing chamber adjacent bore 15. Rod 13 is secured to the outer end of the tube, but it is free of the tube elsewhere. As shown, rod 13 extends into housing chamber 7 beyond the inner end of the tube. Tube 11 and rod 13 are of materials having different coefficients of thermal expansion. For example, tube 11 may be of stainless steel or other metal or alloy, etc., which has a much higher coefficient of thermal expansion than that of the rod. Upon heating the rod-and-tube thermal actuator, both the tube and the rod elongate with the free or outer end of the tube moving away from the housing and with the free or inner end of the rod moving into the housing. Due to the differences in rates of thermal expansion, the outer end of the tube to which rod 13 is secured moves away from the housing a substantially greater distance than the rod elongates. Thus, there is a net outward movement of the inner end of the rod out of the housing (i.e., it is withdrawn therefrom) upon heating of the thermal actuator. An insulative cover 19 closes the mouth of chamber 7.

Briefly, switch means 9 comprises a stationary contact 21, a first terminal 23 for the stationary contact, a movable switch arm 25, a movable contact 27 carried by the switch arm, and a second terminal 29 for the movable contact. The switch arm and the movable contact are movable between a first or closed position (see FIG. 2) in which stationary contact 21 and movable contact 27 are in electrical contact with one another, and a second or open position (see FIG. 3) in which the contacts are spaced from one another for making and breaking an electrical circuit between terminals 23 and 29.

Switch means 9 further includes a switch frame 31 and means, as indicated at 33, for abruptly moving (i.e., snapping) the movable switch arm 25 and contact 27 from their first position (FIG. 2) to their second position (FIG. 3) in response to movement of rod 13 relative to a reference (e. g., relative to housing 3 or stationary contact 21) corresponding to the thermal actuator being exposed to its predetermined trip temperature. Switch frame 31 is secured to cover 19 in contact with terminal 29 by means of a rivet 35. The switch frame comprises a bendable or flexible first portion 37 extending generally parallel to the inner face of cover 19 and has a leg 39 extending downwardly therefrom at one end of the first portion (i.e., the left end portion as viewed in FIGS. 2 and 3) and a Z-shaped support bracket 41 extending down from rivet 35 (see FIG. 5). Bracket 41 fixedly carries a support base 43 for stationary contact 21, the support base being electrically insulated from switch frame 31 by means of a stand-off insulator 45. Insulator 45 is secured to bracket 41 by means of a rivet 47 or other suitable fastener. Support base 43 is carried on the upper end of the stand-off insulator and is insulated from rivet 47 by insulator 45 and by an insulative cover 49. Terminal 23 is secured to cover 19 by a rivet 51 and a flexible lead 53 between support base 43 and rivet 51 so as to connect contact 21 to terminal 23. A stop 54 extends from bracket 41 below contact 21, this stop being engageable by the.

lower face of contact arm 25 when the latter is in its second or open position.

Switch means 9 further includes means coupling rod 13 and switch arm 25 comprising an actuator arm 55 resiliently cantilevered from bracket 41 of switch frame 31 by means of torsion springs 57 secured, as by spot welding, to the underface of the bracket and to the upper face of the actuator arm. Rivet 47 may also be utilized to at least partially secure spring 57 to the bracket. Actuator arm 55 extends above the upper end of rod 13 and out from the lower end of bracket 41. As best shown in FIG. 4, actuator arm 55 is relatively wide at its attachment to springs 57 and its outer end narrows to a width substantially less than the width of switch arm 25. The outer end of actuator 55 is bent up to constitute a vertical leg 59. This bent-up leg 59 is notched, as indicated at 61, to provide a fulcrum for switch arm 25 adjacent leg 59. Actuator arm 55 is slotte'd, as indicated at 63 in FIG. 4, for reception of the lower end of switch frame leg 39.

In FIG. 4, switch arm 25 is shown to be a relatively wide member having a central opening 65. At one end of the switch arm (i.e., at its left end as viewed in FIG. 4) a tab 67 is bent up (see FIGS. 2 and 3) to engage the outer vertical face of leg 59. The engaging edge of tab 67 is set back from the edge of opening 65 so that surfaces 69 of the switch arm adjacent tab 67 engage the sides of leg 59 and substantially prevent lateral movement of the switch arm while permitting the switch arm to pivot on tab 67 for movement between its first and second positions. Also, slots 61 in leg 59 hold the switch arm captive and prevent substantial vertical relative movement between the switch arm and leg 59.

As previously noted, actuator arm 55 is resiliently cantilevered by springs 57 and thus is swingable relative to bracket 41 between a first or upper position (see FIG. 2) and a second or lowered position (see FIG. 3), with the center of the torsion springs 57 constituting a hinge point for the actuating arm. A dimple 71 is formed on the undersurface of the actuating arm for engagement with a rounded insulator 73 carried by the upper end of rod 13. Thus, actuating arm 57 is swingable between its first and second positions in response to movement of rod 13 relative to the housing as the rod-and-tube thermal actuator is heated and cooled. Spring 57 positively biases actuating arm 55 into engagement with insulator 73.

A spring 75 generally U-shaped in cross section, interposed between leg 39 of switch frame 31 and the edge of switch arm 25 defining opening 65 opposite tab 67, constitutes means for abruptly moving switch arm 25 over center between its first and second positions. Spring 75 exerts a force on the switch arm to maintain tab 67 in contact with leg 59 and to bias the switch toward either its first or second position. Switch frame leg 39 is notched, as indicated at 77, for reception of one end of spring 75. As shown in FIG. 4, switch arm 25 has a pair of lugs 79 extending inwardly into opening 65 for reception in corresponding openings (not shown) in spring 75, thereby to positively locate the spring with respect to the switch arm. As may be seen in FIG. 2, with switch arm 25 in its first or raised position and with the contacts 21 and 27 closed, the end of spring 75 received in notch 77 is below an imaginary line extending between the contact of tab 67 and leg 59 and the contact points of lugs 79 and spring 75. Thus, spring 75 biases the switch arm upwardly into engagement with contact 21. As is shown in FIG. 3, with the switch arm in its second or lowered position (i.e., the contacts are opened), notch 77 is above the abovedefined imaginary line so that spring 75 biases the switch arm downwardly into engagement with stop 54. At a centered position (not shown) between its first and second positions, the switch arm is unstable and spring 75 will positively bias it to either its first or second position.

Upon initial movement of actuating arm 55 by rod 13, the end of switch arm 25 in engagement with leg 59 is correspondingly moved in the same direction. However, the other end of the am remains in engagement with its respective contact or stop (i.e., contact 27 remains in engagement with contact 21 or the switch arm remains in contact with stop 54). Continued movement of the actuating arm will cause movement of the tab 67 relative to switch frame notch 77. Upon the line between tab 67 and lugs 69 of switch arm 25 passing through notch 77, spring 75 will abruptly flip the switch arm over center from one position 'to the other. This abrupt snap movement of the switch arm prevents chatter of contacts 21 and 27 which could cause arcing with consequent deleterious effect to the contacts.

It will be noted that, due to the cantilevered construction of actuator arm 55 and the engagement of rod 13 (insulator 73) midway along the length of the actuating rod, leg 59 of the actuating arm moves vertically approximately twice the distance the end of rod 13 moves, thereby increasing or multiplying movement of the outer end of switch arm 25 with respect to movement of rod 13. Furthermore, the manner in which switch arm 25 is supported by tab 67 and tabs 79 causes a multiplication in movement of the end of the switch arm carrying movable contact 27 in response to movement of tab 67. Thus, a relatively small movement of rod 13 with respect to the housing effects multiplied or increased movement of the free end of the contact arm. The fact that switch arm 25 is disposed generally above actuating arm 55 enables efficient and compact packaging of the switch means 9 of this invention and provides positive actuation of the contacts in response to a relatively small movement of rod 13.

The position of rod 13 at which switch arm 25 moves from its first to its second position corresponds to a particular temperature level to which the rod-and-tube actuator 5 is exposed. This temperature may be referred to as the trip temperature. With the switch arm in its second position (FIG. 3), movement of the rod in the opposite direction (i.e., movement into the housing) as occasioned by cooling of the rod-and-tube actuator, to

. another predetermined position, the switch arm will snap over center from its second to its first position when the rod moves into the housing to assume this second predetermined position which corresponds to another temperature level, referred to as the reset temperature. The trip temperature is somewhat higher than the reset temperature, and the difference in these temperatures is referred to as the switch differential temperature.

The switch differential temperature is dependent upon the spacing between contact 21 and stop 54, the closer this spacing the smaller the differential temperature. Upon assembling switch 1 of this invention, the spacing between contact 21 and stop 54 is accurately gauged thereby to establish a predetermined switch differential temperature. If, upon gauging the spacing between contact 21 and stop 54 the spacing is not within a predetermined range, support base 43 carrying stationary contact 21 may be bent toward or away from stop 54 until the appropriate spacing between contact 21 and the stop and the desired switch differential temperature is achieved.

In accordance with this invention, means, as indicated at 80, is provided for adjustably varying the temperature at which switch arm 25 and contact 21 thereon move abruptly over center from one position to another (i.e., from their first or closed position to their second or open position). In other words, means is operable to adjust the trip temperature of switch 1. Means 80 is shown to comprise a screw 81 threaded inan insert 83 carried by cover 19 and positively interconnected to the horizontal portion 37 of switch frame 31. Screw 81 extends exteriorly from housing 5 and cover 19 so that the switch may readily be adjusted without disassembly of the switch. Upon running screw 81 in or out of cover 19, switch frame portion 37 is flexed at its attachment rivet 35 relative to cover 19. This flexing movement causes up-and-down movement of switch frame leg 39 and notch 77 formed therein. As notch 77 is moved up and down, the end of spring 75 cradled therein is moved up and down, thus varying the amount of vertical movement of leg 59 of actuator arm 55 necessary to cause the switch arm 25 to snap over center. By properly calibrating the switch (i.e., by exposing the rod-and-tube thermal actuator 5 to a known temperature condition and by adjusting screw 81 until switch arm 25 moves from its first to its second position), this switch will reliably operate within approximately 1 2% of its desired elevated trip temperature.

As shown in FIG. 5, terminals 23 and 29 have portions 85 and 87, respectively, extending along the underside of cover 17 to provide a convenient electrical connection between terminal 23 and contact 21 and between terminal 29 and switch frame 31. It will be understood that switch frame 31, spring 75, and switch arm 25 carry current to contact 27.

As shown in FIG. 2, switch 1 is normally closed (i.e., its contacts 21 and 27 are closed when thermal actuator 5 is exposed to temperatures below its trip temperature). It will be understood, however, that with suitable minor modifications readily apparent to those skilled in the art (e. g., by insulating stop 54 from switch frame 31 and by connecting a lead between the stop and terminal 23), this switch may be normally open, or made double throw.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A thermally actuated snap-acting switch comprising a switch housing, thermal actuator means having a portion within said housing movable relative thereto in response to changes in temperature, and switch means within the housing actuatable by said thermal actuator means, said switch means comprising a stationary contact, a first terminal for said stationary contact, a switch arm, a movable contact carried by said switch arm, and a second terminal for said movable contact, said switch arm and said movable contact being movable between a first position in which said stationary and said movable contacts are in electrical contact with one another and a second position in which said contacts are spaced from one another for making and breaking an electrical circuit between said terminals, said switch means further comprising a switch frame secured to said housing and means for abruptly moving said switch arm and said movable contact from their first position to their second position when said thermal actuator portion moves into a position corresponding to a predetermined temperature, .said means for abruptly moving said movable contact and said switch arm comprising spring means interposed between said switch arm and said switch frame for biasing said switch arm into one of its positions and for abruptly moving said switch arm between said positions in response to a predetermined amount of movement of said thermal actuator portion, and adjustable means for varyingthe temperature at which said movable contact and switch arm move abruptly over center from one position to another, said adjustable means comprising means for moving said switch frame and said spring means relative to said stationary contact. I

2. A switch as set forth in claim 1 further comprising stop means spaced from said stationary contact engageable by said movable contact when it is in its second position.

3. A switch as set forth in claim 1 wherein said adjustable means extends exteriorly of said housing and is interconnected between said housing and said switch frame so as to adjustably position said switch frame relative to the housing.

4. A switch as set forth in claim 1 wherein said switch means further comprises means interconnecting said thermal actuator and said switch arm for increased movement of the switch arm in response to a given movement of said thermal actuator means.

5. A switch as set forth in claim 4 further comprising spring means biasing said interconnecting means into engagement with said thermal actuator means.

6. A switch as set forth in claim 1 wherein said thermal actuator means comprises a rod-and-tube differential expansion actuator having a tube secured at one end thereof to said housing and extending therefrom and a rod within said tube secured to the other end of the tube, said rod extending into said housing beyond said tube for effecting movement of said switch arm and said movable-contact between their first and second positions.

7. A switch as set forth in claim wherein said tube has a higher coefficient of thermal expansion than said rod whereby, upon heating said tube above a predetermined-trip temperature, said rod moves relative to said housing thereby to effect movement of said switch arm and movable contact from their first to their second positions.

8. A switch as set forth in claim 1 further comprising a stop spaced from said stationary contact a predetermined distance, this distance being adjustable forv varying the differential between said trip and reset temperatures. 1 v

9. A switch as set forth in claim 1 further comprising means coupling said switch arm and said rod whereby a predetermined amount of movement of said rod relative to said housing effects abrupt overcenter movement of said switch arm and said movable contact between their first and second positions, said-coupling means being flexibly secured to said switch housing by means of at least one torsion spring means for biasing said coupling means into engagement withsaid rod. 

1. A thermally actuated snap-acting switch comprising a switch housing, thermal actuator means having a portion within said housing movable relative thereto in response to changes in temperature, and switch means within the housing actuatable by said thermal actuator means, said switch means comprising a stationary contact, a first terminal for said stationary contact, a switch arm, a movable contact carried by said switch arm, and a second terminal for said movable contact, said switch arm and said movable contact being movable between a first position in which said stationary and said movable contacts are in electrical contact with one another and a second position in which said contacts are spaced from one another for making and breaking an electrical circuit between said terminals, said switch means further comprising a switch frame secured to said housing and means for abruptly moving said switch arm and said movable contact from their first position to their second position when said thermal actuator portion moves into a position corresponding to a predetermined temperature, said means for abruptly moving said movable contact and said switch arm comprising spring means interposed between said switch arm and said switch frame for biasing said switch arm into one of its positions and for abruptly moving said switch arm between said positions in response to a predetermined amount of movement of said thermal actuator portion, and adjustable means for varying the temperature at which said movable contact and switch arm move abruptly over center from one position to another, said adjustable means comprising means for moving said switch frame and said spring means relative to said stationary contact.
 2. A switch as set forth in claim 1 further comprising stop means spaced from said stationary contact engageable by said movable contact when it is in its second position.
 3. A switch as set forth in claim 1 wherein said adjustable means extends exteriorly of said housing and is interconnected between said housing and said switch frame so as to adjustably position said switch frame relative to the housing.
 4. A switch as set forth in claim 1 wherein said switch means further comprises means interconnecting said thermal actuator and said switch arm for increased movement of the switch arm in response to a given movement of said thermal actuator means.
 5. A switch as set forth in claim 4 further comprising spring means biasing said interconnecting means into engagement with said thermal actuator means.
 6. A switch as set forth in claim 1 wherein said thermal actuator means comprises a rod-and-tube differential expansion actuator having a tube secured at one end thereof to said housing and extending therefrom and a rod within said tube secured to the other end of the tube, said rod extending into said housing beyond said tube for effecting movement of said switch arm and said movable contact between their first and second positions.
 7. A switch as set forth in claim 6 wherein said tube has a higher coefficient of thermal expansion than said rod whereby, upon heating said tube above a predetermined trip temperature, said rod moves relative to said housing thereby to effect movement of said switch arm and movable contact from their first to their second positions.
 8. A switch as set forth in claim 1 further comprising a stop spaced from said stationary contact a predetermined distance, this distance being adjustable for varying the differential between said trip and reset temperatures.
 9. A switch as set forth in claim 1 further comprising means coupling said switch arm and said rod whereby a predetermined amount of movement of said rod relative to said housing effects abrupt overcenter movement of said switch arm and said movable contact between their first and second positions, said coupling means being flexibly secured to said switch housing by means of at least one torsion spring means for biasing said coupling means into engagement with said rod. 